I. Field of the Invention
This invention relates generally to a novel electrode arrangement for use with an automatic implantable cardioverter/defibrillator (AICD), and more particularly to the design of a highly flexible endocardial lead adapted for placement predominantly in the right ventricle and possessing a shape characteristic and electrode placement for maximizing the energy deliverable to heart tissue during a defibrillation episode.
II. Discussion of the Prior Art
A good synopsis of the prior art relating to electrode arrangements for use with AICD devices is set forth in the section "BACKGROUND OF THE INVENTION" of U.S. Pat. No. 4,662,377 to Heilman et al, which is hereby incorporated by reference. That patent goes on to describe a defibrillating lead in the form of an elongated catheter having a distal tip electrode and with a distal defibrillating electrode insulated therefrom and spaced a short distance proximally thereof. Each of these two electrodes is intended for placement in the right ventricle with the tip electrode disposed in the right apex thereof. A third and more proximal electrode is located at a position which will be within the superior vena cava when the distal tip is at the right ventricular apex. The endocardial lead described in the aforereferenced Heilman et al Patent is intended to cooperate with a flexible patch electrode which is electrically connected to the proximal electrode disposed in the superior vena cava, but the patch itself is positioned between the skin and the rib cage proximate to the left ventricular apex of the heart. When the AICD pulse generator detects a life-threatening, abnormal heart rhythm, it will issue a cardioverting or defibrillating pulse across the distal electrode and the combination of the proximal electrode and the patch electrode.
While the device of the aforereferenced Heilman et al patent affords the advantage of being substantially less traumatic in its placement than systems requiring a thoracotomy, the amount of electrode surface in contact with heart tissue within the right ventricle is necessarily limited. The electrode itself comprised a spring-like arrangement of closely wound turns, e.g., 20 turns per inch, which necessarily adds stiffness or rigidity to the portion of the catheter supporting the electrode surface. As such, it becomes difficult for the electrode area to conform to the interior of the heart and to move in conjunction with the natural contractions of the heart.